1. Field of the Invention
The present invention relates generally to magnetic rotary machines. More particularly, the invention relates to a rotor system for limiting eddy current losses and lowering operating temperature.
2. Discussion of the Background
Magnetic rotary machines include a stator with a rotatable rotor positioned therein and supported by bearings.
The rotor may be subject to eddy current losses caused by magnetic field harmonics. The term eddy current losses means heat generated by eddy currents. Magnetic field harmonics are oscillations in the magnetic field at any frequency other than the fundamental frequency. The term xe2x80x9cwinding harmonicsxe2x80x9d means magnetic field harmonics caused by stator windings. The term xe2x80x9ctooth ripple harmonicsxe2x80x9d are magnetic field harmonics which occur in a stator with teeth, and which depend upon stator tooth-slot spatial distribution.
What is needed is a technique to reduce eddy current losses and lower operating temperature of the magnet.
In one aspect of the invention, a turbogenerator system is described wherein the system includes (1) a turbine mounted for rotation on a shaft; (2) a sleeve coupled with said shaft for rotation therewith; (3) a stator surrounding said sleeve; (4) at least one permanent magnet mounted within said sleeve; and (5) a shield surrounding said at least one permanent magnet, said shield made of electrically conductive nonmagnetic material.
In another aspect of the invention, a generator/motor is described wherein the generator/motor includes (1) a stator; (2) a sleeve mounted for rotation within said stator; (3) at least one permanent magnet positioned within said sleeve for rotation therewith; and (4) a shield surrounding said at least one permanent magnet to rotate therewith, said shield made of electrically conductive nonmagnetic material.
In another aspect of the invention, a permanent magnet apparatus is described wherein the apparatus includes (1) a stator; and (2) a permanent magnet rotor mounted for rotation within said stator, said rotor including a permanent magnet, an electrically conductive nonmagnetic shield and a sleeve.
In another aspect of the invention, a permanent magnet rotor is described wherein the apparatus includes (1) a cylindrical permanent magnet having a cylindrical permanent magnet outer surface; (2) an annular shield having an inner annular surface in contact with said cylindrical permanent magnet outer surface, said annular shield having an annular shield outer surface; (3) an annular sleeve having an annular sleeve inner surface in contact with said annular shield outer surface; and (4) wherein electrical resistivity of said shield is lower than electrical resistivity of said sleeve.
In another aspect of the invention, a method for reducing eddy current losses in a permanent magnet rotor is described wherein the method includes (1) providing a permanent magnet stator; (2) providing a permanent magnet rotor designed to rotate about an axis disposed within said stator, said rotor including a permanent magnet, an electrically conductive nonmagnetic shield and a sleeve, wherein said shield has portions positioned inside said sleeve; and (3) rotating said permanent magnet rotor such that said shield reduces said eddy current losses.
In another aspect of the invention, a method includes (1) providing a cylindrical permanent magnet having a cylindrical permanent magnet outer surface; (2) providing an annular shield having an inner annular surface in contact with said cylindrical permanent magnet outer surface, said annular shield having an annular shield outer surface; (3) providing an annular sleeve having an annular sleeve inner surface in contact with said annular shield outer surface, wherein resistivity of said shield is lower than resistivity of said sleeve; and (4) generating eddy currents in said shield such that said eddy current losses are reduced.